A study on the setting and flow behaviour of alkali activated slag/fly ash composites in ambient condition

Abstract

Alkali-activated binders (AAB) are considered as a promising sustainable future construction material, and promoted as an environmentally beneficial option when compared to Ordinary Portland Cement (OPC). Portland cement-based concrete is the most used material in the construction industry. In the production of OPC, harmful gasses like CO2, NO2, SO2 and specks of dust are discharged into the atmosphere due to calcination of limestone and combustion of fossil fuel. Hence in the present scenario, it has become an emphatic necessity to replace Ordinary Portland Cement based concrete with AAB based system (geopolymer) which is more sustainable. The characteristics of geopolymer composites are predominantly influenced by some of the variables such as temperature and time of curing, alkaline solution to solid binder ratio, water content, type of alkaline activators used, molarity of alkaline solution, chemical composition of aluminosilicate precursors etc. Although geopolymer systems are good in terms of durability and strength, the main issue faced for its less popularity in the field application is its low workability, poor slump retention and too fast setting. The aim of this experimental study is to investigate the compatibility between modern generation superplasticizers (SP) and various alkali activated binder systems prepared using industrial wastes and the evaluation on the effect of alkali binder ratio (a/b) on the fresh properties of alkali activated binder (AAB) systems. Considering the practical implications, it is the need of the hour to develop a geopolymer mix setting in ambient condition. This study focuses on setting and flow behaviour of the alkaline activated composites of slag and fly ash in ambient condition only. The slag/fly ash ratios of 100/0, 75/25, 50/50 and 25/75by mass and alkali-to-binder ratios of 0.4 to 1 with an increment of 0.1 were used for the study. The type of superplasticizer used for the study is Sulphonated Naphthalene Formaldehyde (SNF) with dosages of 0%, 1%, 2% and 3%. The setting time and the flow of the paste were determined using vicat apparatus and mini slump cone respectively. The penetration resistance of the setting paste was also measured using vicat apparatus. The test results revealed that even though the setting time increase marginally with SP dosage, the use of SNF was not much effective in prolonging the setting time of alkali activated pastes. There was tremendous increase in the initial and final setting time for pastes with an increase in a/b ratio.